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Abstract:

A headlamp of the present invention includes: a laser diode for emitting
a laser beam with coherence; and a light emitting section which, upon
irradiation with the laser beam from the laser diode, emits light so that
the light is outputted from the light emitting device. The headlamp
further includes an excitation light output prevention member for
preventing the laser beam from the laser diode from being outputted from
the headlamp while the laser beam maintains coherence.

Claims:

1. A light emitting device, comprising: an excitation light source for
emitting excitation light with coherence; and a light emitting section
which, upon irradiation with the excitation light from the excitation
light source, emits light so that the light is outputted from the light
emitting device, the light emitting device further comprising an
excitation light output prevention member for preventing the excitation
light from the excitation light source from being outputted from the
light emitting device while the excitation light maintains coherence.

2. The light emitting device as set forth in claim 1, wherein the
excitation light output prevention member includes an absorbing member
for absorbing the excitation light with coherence, and the absorbing
member is positioned in a vicinity of the light emitting section in such
a manner as to be closer to an output side of the light emitting device.

3. The light emitting device as set forth in claim 2, further comprising
a mortar-shaped reflection mirror for reflecting the light emitted by the
light emitting section so that the light is directed toward the output
side of the light emitting device, the light emitting section being
positioned inside the mortar-shaped reflection mirror, and the absorbing
member being positioned inside the mortar-shaped reflection mirror in
such a manner as to be in a vicinity of one surface of the light emitting
section which one surface is closer to the output side of the light
emitting device.

4. The light emitting device as set forth in claim 2, further comprising
a mortar-shaped reflection mirror for reflecting the light emitted by the
light emitting section so that the light is directed toward the output
side of the light emitting device, the light emitting section being
positioned inside the mortar-shaped reflection mirror, and the absorbing
member being positioned outside the mortar-shaped reflection mirror.

5. The light emitting device as set forth in claim 4, further comprising
a housing for housing the reflection mirror, the housing having (i) a
light emitting surface for emitting light coming from the reflection
mirror toward the output side of the light emitting device, and (ii) a
light blocking surface for blocking light coming from the reflection
mirror toward a direction different from a direction toward the output
side of the light emitting device, and the absorbing member being
positioned on the light emitting surface of the housing.

6. The light emitting device as set forth in claim 2, further comprising:
a mortar-shaped reflection mirror for reflecting the light emitted by the
light emitting section so that the light is directed toward the output
side of the light emitting device; and a housing for housing the
reflection mirror, the absorbing member including a first absorbing
member and a second absorbing member, the light emitting section being
positioned inside the mortar-shaped reflection mirror, the first
absorbing member being positioned in a vicinity of the light emitting
section in such a manner as to be closer to the output side of the light
emitting device, the housing having (i) a light emitting surface for
emitting light coming from the reflection mirror toward the output side
of the light emitting device, and (ii) a light blocking surface for
blocking light coming from the reflection mirror toward a direction
different from a direction toward the output side of the light emitting
device, and the second absorbing member being positioned on the light
emitting surface of the housing.

7. The light emitting device as set forth in claim 6, wherein the first
absorbing member is positioned inside the mortar-shaped reflection mirror
in such a manner as to be in a vicinity of one surface of the light
emitting section which one surface is closer to the output side of the
light emitting device.

8. The light emitting device as set forth in claim 1, wherein the
excitation light output prevention member includes a scattering member
for scattering the excitation light with coherence.

9. The light emitting device as set forth in claim 8, further comprising
a mortar-shaped reflection mirror for reflecting the light emitted by the
light emitting section so that the light is directed toward an output
side of the light emitting device, the light emitting section being
positioned inside the mortar-shaped reflection mirror, and the scattering
member being positioned inside the mortar-shaped reflection mirror in
such a manner as to be in a vicinity of one surface of the light emitting
section which one surface is closer to the output side of the light
emitting device.

10. The light emitting device as set forth in claim 9, wherein the
scattering member is positioned in a vicinity of the light emitting
section in such a manner as to be closer to the excitation light source,
and the scattering member scatters excitation light coming from the
excitation light source toward the light emitting section, and the light
emitting section is irradiated with the excitation light scattered by the
scattering member.

11. The light emitting device as set forth in claim 8, wherein the
excitation light output prevention member further includes an absorbing
member for absorbing the excitation light with coherence, the excitation
light from the excitation light source enters the scattering member and
the absorbing member in this order, and the absorbing member absorbs
excitation light coming from the excitation light source toward the
output side of the light emitting device regardless of whether the light
emitting section is irradiated with the excitation light.

13. An illuminating equipment comprising a light emitting device as set
forth in claim 1.

14. A vehicle headlamp comprising a light emitting device as set forth in
claim 1.

Description:

[0001] This Nonprovisional application claims priority under 35 U.S.C.
§119(a) on Patent Application No. 2010-244565 filed in Japan on Oct.
29, 2010, the entire contents of which are hereby incorporated by
reference.

TECHNICAL FIELD

[0002] The present invention relates to a light emitting device serving as
a high-intensity light source, to an illuminating equipment including the
light emitting device, and to a vehicle headlamp.

BACKGROUND ART

[0003] In recent years, studies have been intensively carried out for a
light emitting device that uses, as illumination light, fluorescence
generated by a light emitting section which includes a fluorescent
material. The light emitting section generates the fluorescence upon
irradiation with excitation light, which is emitted from an excitation
light source. The excitation light source used is a semiconductor light
emitting element, such as a light emitting diode (LED), a laser diode
(LD), or the like.

[0004] An example of a technique relating to such a light emitting device
is a lamp disclosed in Patent Literature 1. In order to achieve a
high-luminance light source, the lamp employs a laser diode as an
excitation light source. Since a laser beam emitted from the laser diode
is coherent and therefore highly directional, the laser beam can be
collected without a loss so as to be used as excitation light. The light
emitting device employing such a laser diode as the excitation light
source is suitably applicable to a vehicle headlamp.

[0005] In particular, the lamp of Patent Literature 1 is designed such
that the semiconductor light emitting element emits ultraviolet light and
the fluorescent material emits white light in response to the ultraviolet
light. The fluorescent material can emit white light with high luminance.
The fluorescent material produces white diffusing light in response to
the ultraviolet light.

[0006] The lamp includes a transparent member positioned before the
fluorescent material. The transparent member is made of a material which
transmits white light and blocks ultraviolet light.

[0007] The transparent member transmits light from the fluorescent
material toward the front of a vehicle, whereas blocks ultraviolet light
which is emitted from the semiconductor light emitting element and
harmful to a human body from being outputted outside the vehicle.

[0008] Alternatively, the transparent member itself may be made of a
material that transmits ultraviolet light and is provided, on a front
surface of the transparent member, with a member which blocks ultraviolet
light.

[0010] As described above, in the lamp of Patent Literature 1, ultraviolet
light from the semiconductor light emitting element is blocked so as not
to be outputted outside the vehicle. Since ultraviolet light is
invisible, illumination light is not required to include ultraviolet
light, and so all the ultraviolet light may be blocked simply.

[0011] Further, it is generally known that ultraviolet light has adverse
effects on eyes and skins. An example of the adverse effects of
ultraviolet light on eyes is keratitis (e.g. inflammation of a cornea on
the uppermost surface of an eyeball). Examples of the adverse effects of
ultraviolet light on skins include sunburn and deterioration of DNA
possibly inducing skin cancers.

[0012] Accordingly, the lamp is required to block ultraviolet light.

[0013] A laser beam from a semiconductor light emitting element is
coherent light. Coherent light can be roughly classified into two kinds:
invisible coherent light (light with a wavelength in an ultraviolet range
or infrared range); and visible coherent light (light with a wavelength
in a visible range).

[0014] Coherent light can be easily converged onto an extremely small spot
by an optical system such as a lens, and can locally have extremely high
energy. Accordingly, when coherent light enters eyes for example, there
is a possibility that a pinpoint on a retina is irradiated with converged
light and concentration of light energy on the pinpoint hurts optical
nerves.

[0015] In consideration of such characteristics of coherent light, it is
necessary to block coherent light with a wavelength in a visible range as
well as coherent light with a wavelength in an ultraviolet range or
infrared range including ultraviolet light.

[0016] In general, coherent light is defined as light with spatially and
temporally uniform phase, and has a single-wavelength. Accordingly, a
member for blocking coherent light should be a member which blocks only
wavelength and its adjacent ones of the coherent light.

[0017] In a case of blocking coherent light in a visible range, blocking a
wavelength range broader than necessary would also block much of light
necessary as illumination light other than the coherent light.
Accordingly, it is important to make a wavelength range to be blocked as
narrow as possible so that only a wavelength range in which the coherent
light is presented is blocked.

[0019] The present invention was made in view of the foregoing problem. An
object of the present invention is to provide a light emitting device
capable of preventing coherent light from being outputted outside, and an
illuminating equipment and a vehicle headlamp each including the light
emitting device.

Solution to Problem

[0020] In order to solve the foregoing problem, a light emitting device of
the present invention includes: an excitation light source for emitting
excitation light with coherence; and a light emitting section which, upon
irradiation with the excitation light from the excitation light source,
emits light so that the light is outputted from the light emitting
device, the light emitting device further including an excitation light
output prevention member for preventing the excitation light from the
excitation light source from being outputted from the light emitting
device while the excitation light maintains coherence.

[0021] With the light emitting device, the light emitting section emits
light upon irradiation with the excitation light. When the light emitting
section emits light, coherence of the excitation light with which the
light emitting section is irradiated is normally reduced sufficiently by
absorption and/or scattering by the fluorescent material contained in the
light emitting section.

[0022] However, some of the excitation light from the excitation light
source may be not used in emission by the light emitting section and
travel toward the output side of the light emitting device while
maintaining coherence in a level which has an adverse influence on human
bodies.

[0023] Examples of such excitation light which comes from the excitation
light source and travels toward the output side of the light emitting
device while maintaining coherence include: (a) excitation light with
which the light emitting section is not irradiated; (b) excitation light
with which the light emitting section is irradiated but which is neither
absorbed nor scattered by the fluorescent material contained in the light
emitting section so that the excitation light is outputted from the light
emitting section without any change; (c) excitation light with which the
light emitting section is irradiated but which is reflected by the
surface of the light emitting section so that the excitation light is
outputted while substantially maintaining coherence.

[0024] In a case where the excitation light with coherence in a level
which has an adverse influence on human bodies is outputted from the
light emitting device without any change, when the excitation light
enters human eyes, there is a possibility that a pinpoint on a retina is
irradiated with converged light and concentration of light energy on the
pinpoint hurts optic nerves.

[0025] In order to deal with this problem, the light emitting device of
the present invention includes the excitation light output prevention
member which prevents the excitation light with coherence from being
outputted from the light emitting device without any change.

Advantageous Effects of Invention

[0026] As described above, a light emitting device of the present
invention includes: an excitation light source for emitting excitation
light with coherence; and a light emitting section which, upon
irradiation with the excitation light from the excitation light source,
emits light so that the light is outputted from the light emitting
device, the light emitting device further including an excitation light
output prevention member for preventing the excitation light from the
excitation light source from being outputted from the light emitting
device while the excitation light maintains coherence.

[0027] Therefore, the light emitting device of the present invention
yields an effect of preventing the coherent light from being outputted
outside.

BRIEF DESCRIPTION OF DRAWINGS

[0028]FIG. 1 is a view schematically showing a configuration of a
headlamp according to one embodiment of the present invention.

[0029]FIG. 2 is a view showing an effect of an excitation-light output
prevention film included in the headlamp (version 1).

[0030]FIG. 3 is a view showing an effect of the excitation-light output
prevention film included in the headlamp (version 2).

[0031]FIG. 4 is a cross sectional view schematically showing a
configuration of the excitation-light output prevention film included in
the headlamp.

[0032]FIG. 5 is a view schematically showing a configuration of a
headlamp according to another embodiment of the present invention.

[0034]FIG. 6(b) is a perspective view showing a basic structure of the
laser diode.

[0035]FIG. 7 is a view schematically showing (i) an exterior of a
light-emitting unit included in a laser downlight according to the
embodiment of the present invention and (ii) an exterior of a
conventional LED downlight.

[0036] FIG. 8 is a cross sectional view showing a ceiling to which the
laser downlight is installed.

[0038]FIG. 10 is a cross sectional view showing a modified example of a
method for installing the laser downlight.

[0039] FIG. 11 is a cross sectional view showing a ceiling to which the
LED downlight is installed.

[0040]FIG. 12 is a table in which specifications of the laser downlight
and those of the LED downlight are compared with each other.

DESCRIPTION OF EMBODIMENTS

Embodiment 1

[0041] One embodiment of the present invention is described below with
reference to FIGS. 1 through 4. In the present embodiment, a headlamp 1
satisfying light distribution property standards for a driving headlamp
(high beam) for use in an automobile is described as an example of an
illuminating equipment according to the present invention. Note, however,
that the illuminating equipment of the present invention can be achieved
also as a headlamp which meets the light distribution property standards
of a passing headlamp (low beam) for an automobile or a headlamp for a
vehicle other than the automobile or for a moving object other than the
automobile (e.g., a person, a vessel, an airplane, a submersible vessel,
or a rocket) or can be achieved as other illuminating equipment. Examples
of the other illuminating equipment include a searchlight, a projector,
and lighting equipment for housing.

[0042] (Configuration of Headlamp 1)

[0043] With reference to FIG. 1, the following describes a configuration
of the headlamp 1 (illuminating equipment) 1 according to the present
embodiment. FIG. 1 is a view schematically showing the configuration of
the headlamp 1 according to the present embodiment. As shown in FIG. 1,
the headlamp 1 includes a laser diode (excitation light source) 3, an
aspheric lens 4, a light guide section 2, a light emitting section 7, a
reflection mirror 8, a transparent plate 9, a housing 11, and an
excitation-light output prevention film (excitation-light output
prevention member, absorbent member, scattering member) 12.

[0044] (Laser Diode 3)

[0045] The laser diode 3 functions as an excitation light source for
emitting excitation light. The laser diode 3 emits a laser beam
(excitation light). The laser diode 3 can be provided in plural numbers.
In such an event, each of a plurality of laser diodes 3 emits a laser
beam.

[0046] The excitation light emitted from the laser diode 3 is coherent
light having coherence. As described early, the coherent light is
generally light being spatially and temporally in phase. A wavelength of
the coherent light is a single wavelength.

[0047] The laser diode 3 has ten light emitting points (ten stripes) per
chip. For example, the laser diode 3 emits a laser beam of 405 nm (blue
violet), has an output of 11.2 W, an operating voltage of 5 V and an
operating current of 6.4 A, and is mounted on a stem having a diameter of
15 mm. In a case where the laser diode 3 is caused to emit a laser beam
at the output of 11.2 W, an electric power consumption of the laser diode
is 32 W (5 V×6.4 A). Obviously, the laser beam emitted from the
laser diode 3 is not limited to 405 nm, and may be any laser beam as long
as the laser beam has a peak wavelength in a wavelength range of 400 nm
or greater but not greater than 420 nm.

[0048] In a case where three laser diodes 3 are mounted, for example, an
optical output (emission bundle) of the laser diodes 3 as a whole is 33.6
W and an electric power consumption thereof is 96 W (=5 V×6.4
A×3). In order to obtain a laser beam of a high output, it is
preferable to use a plurality of laser diodes 3.

[0049] The aspheric lens 4 is a lens for receiving the laser beam emitted
from the laser diode 3 and entering it in a light entrance surface 21,
i.e., a first end part, of the light guide section 2. For example, FLKN1
405 manufactured by ALPS ELECTRIC CO., LTD. can be used as the aspheric
lens 4. The aspheric lens 4 is not particularly limited in shape and
material, provided that it has the foregoing function. However, it is
preferable that a material of the aspheric lens 4 has (i) a high
transmittance with respect to light at and around a wavelength of 405 nm
which is the wavelength of the excitation light and (ii) a good heat
resistance.

[0050] (Light Guide Section 2)

[0051] The light guide section 2 is for converging the laser beam emitted
from the laser diode 3 and guiding it to a laser-beam irradiation surface
7a of the light emitting section 7. The light guide section 2 is a light
guide member of a trapezoid shape having a rectangular bottom surface and
being tapered. The light guide section 2 is optically combined with the
laser diode 3 via the aspheric lens 4. The light guide section 2 has (i)
the light entrance surface 21 for receiving the laser beam emitted from
the laser diode 3 and (ii) a light output surface 22 for outputting,
toward the light emitting section 7, the laser beam received on the light
entrance surface 21. That is, the light guide section 2 has the light
entrance surface 21 provided at a bottom part and the light output
surface 22 provided at a top part.

[0052] The light output surface 22 has an area smaller than that of the
light entrance surface 21. Accordingly, the laser beam which has entered
the light entrance surface 21 is converged by traveling forward while
being reflected on side surfaces 23 of the light guide section 4. The
laser beam thus converged is emitted from the light output surface 22.

[0053] The area of the light entrance surface 21 is 15 mm×3 mm and
the area of the light output surface 22 is 3 mm×1 mm, for example.
A height of the light guide section 2, in other words, a distance between
the light entrance surface 21 and the light output surface 22, is 50 mm,
for example. The side surfaces 23 of the light guide 2 are coated with a
fluororesin (polytetrafluoroethylene) having a refraction index of 1.35.
The side surfaces 23 thus coated with the fluororesin can efficiently
reflect a laser beam. This is because the fluororesin and a transparent
material forming the light guide section 2 have different refraction
indices.

[0054] The light output surface 22 may be a planoconvex cylindrical lens
whose axis runs in a direction vertical to an axis passing through the
light entrance surface 21 and the light output surface 22. That is, the
light output surface 22 may have a curved surface shape. In such an
event, the laser beam is emitted from the light output surface 22 so as
to spread at a given angle. In this way, the laser beam emitted from the
light output surface 22 is dispersed. Accordingly, the laser beam
irradiation surface 7a is irradiated with the laser beam thus dispersed,
instead that one spot of the laser beam irradiation surface 7a is
concentratedly irradiated with the laser beam. This makes it possible to
prevent the light emitting section 7 from being deteriorated by
concentric irradiation of the one spot of the laser beam irradiation
surface 7a with the laser beam. Therefore, it is possible to realize the
headlamp 1 which has a high light flux, a high brightness, and an
extended operating life.

[0055] In the present embodiment, the light output surface 22 functions as
a cylindrical lens. Alternatively, the light output surface 22 may be
provided with an independent cylindrical lens. In such an event, the
independent cylindrical lens is provided between the light output surface
22 and the light emitting section 7.

[0056] Specifically, the light guide section 2 is made from silica glass
(SiO2, refractive index of 1.45), an acrylic resin, or other
transparent materials. The light entrance surface 21 may have a planar
shape or a curved surface shape.

[0057] A coupling efficiency of the aspheric lens 4 and the light guide
section 2 (a ratio of an intensity of the laser beam emitted from the
light output surface 22 of the light guide section 2 with respect to an
intensity of the laser beam emitted from the laser diode 3) is 90%.
Consequently, a power of a laser beam of about 11.2 W emitted from the
laser diode 3 will be about 10 W when the laser beam is emitted from the
light output surface 22 after passing through the aspheric lens 4 and the
light guide section 2.

[0058] (Light Emitting Section 7)

[0059] The light emitting section 7 emits light upon irradiation with the
laser beam emitted from the laser output surface 22. The light emitting
section 7 includes fluorescent materials that emit light upon irradiation
with the laser beam. The light emitting section 7 is provided on an
inward side (a side on which the 22 is provided) of the transparent plate
9 so as to be fixed to or near a focal position of the reflection mirror
9. A method for fixing the light emitting section 7 is not limited to
this, and the light emitting section 7 may be fixed by a rod-like or
tubular member extended from the reflection mirror 8.

[0060] As described above, the light emitting section 7 emits light upon
the irradiation with the laser beam. The laser beam is coherent light
emitted from the laser diode 3. The light emitting section 7 is
irradiated with the coherent light and emits incoherent light (white
light) not having coherence.

[0061] The light emitting section 7 is described in detail later.

[0062] (Reflection Mirror 8)

[0063] The reflection mirror 8 has an opening. The reflection mirror 8
reflects the incoherent light emitted from the light emitting section 7,
thereby forming a bundle of beams traveling within a predetermined solid
angle to be emitted via the opening. That is, the reflection mirror 8
reflects light emitted from the light emitting section 7, thereby forming
a bundle of beams traveling in a forward direction from the headlamp 1.
That is, the reflection mirror 8 outputs the bundle of beams toward an
output side of the headlamp 1. For example, the reflection mirror 8 is a
member having a curved surface (cup shape, mortar shape) coated with a
metal thin film. The opening of the reflection mirror 8 opens toward a
direction in which the reflected light travels.

[0064] The reflection mirror 8 is not limited to a hemispherical mirror,
but may be an ellipsoidal mirror, a parabola mirror, or a mirror having a
partial curved surface of the hemispherical mirror, the ellipsoidal
mirror, and/or the parabola mirror. That is, the reflection mirror 8 may
be any, provided that its reflection surface has at least a part of a
curved surface formed by rotating a figure (ellipsoid, circle, or
parabola) on a rotation axis. Also, the opening of the reflection mirror
8 is not limited to a circular shape. The shape of the opening of the
reflection mirror 8 can be determined as appropriate, depending on
designs of the headlamp 1 and a member surrounding it.

[0065] An area of the reflection mirror 8 with respect to a front
direction is called an opening area of the reflection mirror 8. The
opening area is the area of an image of the reflection mirror 8 projected
on a plane perpendicular to the optical axis of the reflection mirror 8.
In still other words, the opening area is the area of a region surrounded
by the opening of the reflection mirror 8 (region shown by a reference
sign 8a in FIG. 1). Smallness in the opening area indicates smallness in
the reflection mirror 8, resulting in smallness in the headlamp 1. In
order for the headlamp 1 to be small, it is preferable that the opening
area of the reflection mirror 8 be not greater than 2000 mm2.

[0066] The transparent plate 9 is a transparent resin plate covering the
opening of the reflection mirror 8. The transparent plate 9 is for
holding the light emitting section 7. The transparent plate 9 is made
from a material that transmits therethrough any of coherent light and
incoherent light as described earlier. Accordingly, the transparent plate
9 may be made from any transparent material. This can make it easier and
less costly to produce the transparent plate 9.

[0067] Obviously, the transparent plate 9 can be omitted in a case where,
as described earlier, the light emitting section 7 is held by a member
other than the transparent plate 9, such as the rod-like or tubular
member extended from the reflection mirror 8.

[0068] (Composition of Light Emitting Section 7)

[0069] The light emitting section 7 is a member in which a fluorescent
material is dispersed inside a silicone resin that serves as a
fluorescent material retention substance. A ratio of the silicone resin
to the fluorescent material is around 10:1. The light emitting section 7
may be formed by pressing the fluorescent material into a solid. The
fluorescent material retention substance is not limited to the silicone
resin and may be organic-inorganic hybrid glass or inorganic glass.

[0070] The fluorescent material is, for example, any of an
oxynitride-based fluorescent material and a nitride-based fluorescent
material, or a combination thereof. The fluorescent materials of blue,
green, and red are dispersed in the silicone resin. Because the laser
diode 3 emits a laser beam of 405 nm (blue violet), the light emitting
section 7 emits, upon irradiation with the laser beam, white light. On
this account, it can be said that the light emitting section 7 is a
wavelength conversion material.

[0071] The laser diode 3 may emit a laser beam of 450 nm (blue) (or a
laser beam close to so-called "blue" having a peak wavelength in a
wavelength range of 440 nm or greater but not greater than 490 nm). In
this case, the fluorescent material is a yellow fluorescent material or a
mixture of green and red fluorescent materials. The yellow fluorescent
material is a fluorescent material which emits light having a peak
wavelength in a wavelength range of 560 nm or greater but not greater
than 590 nm. The green fluorescent material is a fluorescent material
which emits light having a peak wavelength in a wavelength range of 510
nm or greater but not greater than 560 nm. The red fluorescent material
is a fluorescent material which emits light having a peak wavelength in a
wavelength range of 600 nm or greater but not greater than 680 nm.

[0072] The fluorescent material is preferably what is commonly called a
sialon fluorescent material (which is one type of nitride fluorescent
materials). The sialon fluorescent material is a substance in which a
part of silicon atoms of silicon nitride is substituted by aluminum
atoms, and a part of nitrogen atoms of the silicon nitride is substituted
by oxygen atoms. The sialon fluorescent material may be prepared by a
solid solution in which alumina (Al2O3), silica (SiO2),
rare earth elements, and the like are combined into silicon nitride
(Si3N4).

[0073] Another preferable example of the fluorescent material is a
semiconductor nanoparticle fluorescent material using nanometer-sized
particles of a III-V compound semiconductor.

[0074] One characteristic of the semiconductor nanoparticle fluorescent
material is that, even if the nanoparticles are made from an identical
compound semiconductor (e.g., indium fluorescent materials: InP), it is
possible to cause the nanoparticles to emit light of different colors by
changing particle size of the nanoparticles. The change in color occurs
due to a quantum size effect. For example, in a case where the
semiconductor nanoparticle fluorescent material is made from InP, the
semiconductor nanoparticle fluorescent material with a particle size of
about 3 nm to 4 nm emit red light. The particle size is evaluated by use
of a transmission electron microscope (TEM).

[0075] Further, the semiconductor nanoparticle fluorescent material is
semiconductor-based, and therefore the life of the fluorescence is short.
Accordingly, the semiconductor nanoparticle fluorescent material can
quickly convert power of the excitation light into fluorescence, and
therefore is highly resistant to high-power excitation light. This is
because the emission life of the semiconductor nanoparticle fluorescent
material is approximately 10 nanoseconds, which is less by five digits
than emission life of a commonly used fluorescent material containing
rare earth as a luminescence center.

[0076] In addition, since the emission life is short as described above,
it is possible to quickly repeat absorption of a laser beam and emission
of fluorescence. As such, it is possible to maintain high conversion
efficiency with respect to intense laser beams, thereby reducing heat
emission from the fluorescent materials.

[0077] This makes it possible to further prevent a heat deterioration
(discoloration and/or deformation) in the light emitting section 7. As
such, it is possible to extend the life of the headlamp 1.

[0078] (Shape and Size of Light Emitting Section 7)

[0079] The light emitting section 7 has a rectangular parallelepiped shape
of dimensions of 3 mm×1 mm×1 mm, for example. In this case,
an area of the laser beam irradiation surface 7a which receives the laser
beam emitted from the laser diode 3 is 3 mm2, and an area of the
light emitting surface 7b from which the white light converted from the
laser beam is emitted is 3 mm2. A light distribution pattern (light
distribution) of a vehicle headlamp lawfully stipulated domestically in
Japan is narrow in a vertical direction and broad in a horizontal
direction. Hence, if the light emitting section 7 is configured to have a
shape wide in the horizontal direction (i.e., a cross section of the
light emitting section 7 is a substantially rectangular shape), it is
easier to achieve the distribution pattern.

[0080] The light emitting section 7 may have a shape other than the
rectangular parallelepiped shape. The light emitting section 7 may have a
cylindrical shape in which the laser beam irradiation surface 7a and the
light emitting surface 7b have circular or ellipsoid shapes. The light
emitting surface 7b does not necessarily have a planar surface and may
have a curved surface. In a case where the laser beam irradiation surface
7a is curved, at least angles of incidence on the laser beam irradiation
surface 7a are greatly varied. Consequently, the direction in which the
reflected light travels is greatly varied depending on where the laser
beam enters the laser irradiation surface 7a. For this reason, there is a
case that it is difficult to control a direction in which the laser beam
is reflected. On the other hand, in a case where the laser beam
irradiation surface 7a is planar, it is easier to control the direction
in which the laser beam is reflected. This is because, with the laser
beam irradiation surface 7a being planar, directions in which reflected
light travels are hardly varied irrespectively of slight variations in
where the laser beam enters the laser beam irradiation surface 7a.
Consequently, it is easier to take measures such as to provide, depending
on circumstances, a laser beam absorber at a location where the reflected
light is incident, or the like.

[0081] Further, a thickness of the light emitting section 7, i.e., a width
extended between the laser beam irradiation surface 7a and the light
emitting surface 7b, may be other than 1 mm. The thickness of the light
emitting section 7 should be such a thickness that the laser beam
received by the laser beam irradiation surface 7a is completely converted
to white light by the light emitting section 7 or sufficiently scattered
by the light emitting section 7. The light emitting section 7 should have
such a thickness that coherent light which is harmful to human bodies is
converted to incoherent light harmless to humans or to coherent light in
a level which does not have an adverse influence on human bodies.

[0082] A required thickness of the light emitting section 7 is changed
depending on the ratio of the fluorescent material retention substance to
the fluorescent material in the light emitting section 7. The greater a
content of the fluorescent material in the light emitting section 7 is,
the greater an efficiency of conversion of the laser beam into the white
light is. Thus, the light emitting section 7 can be reduced in thickness.

[0083] (Housing 11)

[0084] The housing 11 houses therein the laser diode 3, the aspheric lens
4, the light guide section 2, the light emitting section 7, the
reflection mirror 8, and the transparent plate 9. The housing 11 is
sealed. An inside of the housing 11 is filled with a dry air, for
example. the dry air has a dew-point temperature of -35° C. for
example and thus prevents increases in temperatures of the laser diode 3
and the light emitting section 7.

[0085] Two electrode lead wires which are provided to the laser diode 3
are outwardly extended from the housing 11 so as to be connected with a
laser drive circuit (which is not shown in figures). The laser drive
circuit supplies a driving current to the laser diode 3 by continuously
or intermittently applying a predetermined voltage difference across the
two electrode lead wires.

[0086] The housing 11 has a front surface section (output surface) 11a.
Similarly to the transparent plate 9 described earlier, the front end
section 11a is made from a material that transmits therethrough both
coherent light and incoherent light. The front end section 11a faces the
surface 8a surrounded by the opening of the reflection mirror 8. The
front end section 11a transmits therethrough the bundle of beams having
been formed by the reflection mirror 8 and emitted from the surface 8a.
In consideration of transmission of the bundle of beams, the front end
section 11a may be configured such that only a part of the front end
section 11a, through which part the bundle of beams emitted from the
surfaces 8a of the reflection mirror 8 is transmitted, is made from the
transmitting material described above.

[0087] The front end section 11a of the housing 11 can be made from any
transparent material. This can make it easier and less costly to produce
the front end section 11a.

[0088] Other surfaces (lightproof surfaces) of the housing 11 than the
front surface section 11 should be formed by a lightproof member that
blocks both coherent light and incoherent light.

[0089] (Excitation-Light Output Prevention Film 12)

[0090] The excitation-light output prevention film 12 is attached to the
front end section 11a of the housing 11. In this case, it can be said
that the excitation-light output prevention film 12 is provided on the
output side of the headlamp 1 when seen from the light emitting section
7, as shown in FIG. 1.

[0091] As described above, the headlamp 1 outputs the bundle of beams
formed by the reflection mirror 8 and passed through (i) the transparent
plate 9 covering the opening of the reflection mirror 8 and (ii) the
front end section 11a of the housing 11.

[0092] The bundle of beams formed by the reflection mirror 8 is composed
of the light emitted from the light emitting section 7 and having no
coherence, i.e., incoherent light. Thus, usually, no coherent light is
leaked outside the headlamp 1 even in a case where both the transparent
plate 9 and the front end section 11a of the housing 11 are made from the
transparent material which transmits therethrough both the coherent light
and the incoherent light. This is because, the laser beam emitted from
the laser diode 3, i.e., the coherent light, should be directed to the
light emitting section 7 and thereby converted to the incoherent light by
the light emitting section 7.

[0093] However, in reality, there may be a case that the bundle of beams
formed by the reflection mirror 8 contains the coherent light. The
excitation-light output prevention film 12, in preparation for such an
event, takes a role in prevention of leakage of the coherent light
outwardly from the headlamp 1. That is, in the case where the bundle of
beams formed by the reflection mirror 8 contains the coherent light, the
excitation-light output prevention film 12 weakens and blocks the
coherent light received thereon, so as to prevent the coherent light from
being leaked outwardly from the headlamp 1.

[0094] For example, in the headlamp 1a as shown in FIG. 2, the laser beam
emitted from the light output surface 22 of the light guide section 2 is
usually directed to the light emitting section 7, like a laser beam
indicated by a reference sign 31. Then, the laser beam 31 is absorbed by
the fluorescent material contained in the light emitting section 7, and
thereby converted in wavelength. While this occurs, coherence of the
laser beam 31 is lost.

[0095] In this case, the bundle of beams formed by the reflection mirror 8
is composed of fluorescent light 32 thus having no coherence. As a
result, the bundle of beams must contain no coherent light.

[0096] On the other hand, a laser beam indicated by a reference sign 33,
out of the laser beam emitted from the light output surface 22 of the
light guide section 2, enters no light emitting section 7 while traveling
in a direction in which it is emitted from the light output surface 22.
This is highly likely the case, depending on a shape of the light output
surface 22 of the light guide section 2, a shape of a light entrance
opening of the reflection mirror 8 via which light entrance opening the
laser beam emitted from the light output surface 22 passes, a location, a
size, a shape, and the like of the light emitting section 7.

[0097] In such an event, the laser beam 33 that maintains the coherence
enters no light emitting section 7 and is transmitted through the
transparent plate 9 and the front end section 11a of the housing 11. This
is because both the transparent plate 9 and the front end section 11a are
made from the transparent material that transmits therethrough even the
coherent light.

[0098] For another example, in a headlamp 1b as shown in FIG. 3, a laser
beam emitted from a light output surface 22 of a light guide section 2 is
directed to a light emitting section 7 and usually absorbed by a
fluorescent material contained in the light emitting section 7, like a
laser beam indicated by a reference sign 34. A wavelength of the laser
beam 34 thus absorbed is converted. Coherence of the laser beam 34 is
lost at the same time when the wavelength of the laser beam 34 is
converted

[0099] In this case, a bundle of beams formed by a reflection mirror 8 is
composed of fluorescent light 35 thus having no coherence. As a result,
the bundle of beams must contain no coherent light.

[0100] On the other hand, although a laser beam indicated by a reference
sign 36, out of the laser beam emitted from the light output surface 22
of the light guide section 2, is directed to the light emitting section
7, the laser beam indicated by the reference sign 36 is not absorbed by
the fluorescent material contained in the light emitting section 7 and
thereby emitted from the light emitting section 7.

[0101] Here, even if the laser beam emitted from the light output surface
22 is not absorbed by any of the fluorescent materials contained in the
light emitting section 7, it is usually scattered by some of the
fluorescent materials.

[0102] However, there may be a case that some portion of the laser beam
directed to the light emitting section 7 is neither absorbed nor
scattered by the fluorescent material contained in the light emitting
section 7, depending on a path on which the laser beam is transmitted
through an inside of the light emitting section 7 and/or depending on a
dispersion distribution of the fluorescent material contained inside the
light emitting section 7.

[0103] In such an event, although the laser beam 36 is directed to the
light emitting section 7, the laser beam 36 is neither absorbed nor
scattered by the fluorescent materials contained in the light emitting
section 7 and is thereby emitted from the light emitting section 7. That
is, the laser beam 36 that maintains coherence is emitted from the light
emitting section 7.

[0104] Thereafter, the laser beam 36 maintaining the coherence is
transmitted through the transparent plate 9 and the front end section 11a
of the housing 11.

[0105] In this way, there is a case that the bundle of beams formed by the
reflection mirror 8 contains coherent light.

[0106] As described earlier, the excitation-light output prevention film
12 is attached to the front end section 11a of the housing 11. The
excitation-light output prevention film 12 has an excitation-light output
prevention function (which is later described) that dissolves the
coherence of a bundle of beams passing through the excitation-light
output prevention film 12.

[0107] As a result of the excitation-light output prevention function, the
excitation-light output prevention film 12 attenuates and blocks the
coherent light contained in the bundle of beams transmitted through the
transparent plate 9 and the front end section 11a of the housing 11 as
above. Thus, even if the bundle of beams formed by the reflection mirror
8 contains the coherent light, it is possible to prevent the coherent
light from being leaked outside the headlamp 1 while the coherent light
is maintained in a level which has an adverse influence on human bodies.

[0108] Concrete examples of the excitation-light output prevention film 12
are described below.

[0109] For example, the excitation-light output prevention film 12 can be
an optical film that attenuates and blocks a light component having a
wavelength of at least 400 nm or greater but not greater 420 nm. An
example of the optical film can be UV Guard manufactured by NAIGAI
TECHNOS Co., jp Ltd. FIG. 4 schematically shows a configuration of the
excitation-light output prevention film 12 that is the optical film.

[0110] As shown in FIG. 4, the excitation-light output prevention film 12
includes (i) an adhesive layer 12a provided on and in direct contact with
an exfoliative film 13, (ii) a light cutting layer 12b that blocks light
having a wavelength of 420 nm or smaller, (iii) a PET base 12c, and (iv)
a hard coat layer 12d, which are provided in this order.

[0111] The adhesive layer 12a is for attaching the excitation-light output
prevention film 12 to the front end section 11a of the housing 11. In
order to maintain adhesiveness of the adhesive layer 12 before the
adhesive layer 12 is attached to the front end section 11a of the housing
11, an adhesive surface of the adhesive layer 12a is protected using the
exfoliative film 13.

[0112] In order for the adhesive layer 12a to have adhesiveness, a
conventional adhesive agent is applied to the adhesive surface of the
adhesive layer 12a that adheres to the front end section 11a of the
housing 11.

[0113] The light cutting layer 12b is prepared by dispersing, in a
thermoplastic polyester (polyethylene terephthalate) resin having a
thickness of 100 μm, a light absorbing agent for absorbing light
having a wavelength of 420 nm or less. The light absorbing agent for
absorbing light having a wavelength of 420 nm or less may be of an
organic molecule having a benzene ring, such as a benzophenone- or
benzoate-based molecule, a benzotriazole-based molecule, a triazine-based
molecule, and the like. Light with a desired wavelength or less can be
cut depending on densities of such organic molecules or combinations of
the organic molecules.

[0114] The PET base 12c is a polymer film made from a thermoplastic
polyester resin and having a thickness of 50 μm. The hard coat layer
12d is made from an optically or thermally reactive curable resin
composition and has a thickness of 10 μm.

[0115] The excitation-light output prevention film 12 is attached to an
inward side of the front end section 11a of the housing 11 by removing
the exfoliative film 13, for example. Obviously, the excitation-light
output prevention film 12 may be alternatively attached to an outward
side of the front end section 11a of the housing 11. In this case,
however, it is preferred that the adhesive layer 12a also contains an
ultraviolet absorber dispersed therein so that no light having an intense
wavelength of 450 nm or smaller directly enters the PET base 12c.

[0116] For another example, the excitation-light output prevention film 12
may be an optical film that scatters a light component having a
wavelength of at least 400 nm or greater but not greater than 420 nm.
Examples of the optical film encompass a so-called "frosted glass" having
asperities formed on a surface and a film having fine particles of
different refractive indices dispersed inside the film.

[0117] As described above, the excitation-light output prevention film 12
is an absorption film (absorption member) for absorbing coherent light
maintaining coherence or a scattering film (scattering member) for
scattering the coherent light maintaining coherence. Use of such films as
the excitation-light output film 12 realizes the excitation-light output
prevention function. Obviously, the excitation-light output prevention
film 12 may be any one of the absorption film and the scattering film or
a combination thereof.

[0118] The laser diode 3 of the headlamp 1 in accordance with the present
embodiment may be a laser diode that emits a laser beam having a
wavelength of 400 nm or greater but not greater than 420 nm, as described
above.

[0119] A laser beam having a wavelength of less than 400 nm has a low
visibility. As such, in a case where the laser diode 3 is a laser diode
that emits a laser beam having a wavelength of less than 400 nm,
especially less than 380 nm, for example, there is a risk that even if
the laser beam emitted from the laser diode is leaked outside the
headlamp 1 in the above described way, a leakage of the laser beam is not
recognized by anyone.

[0120] Further, a laser diode beam having a wavelength of less than 380 nm
and thereby falling in an (near-)ultraviolet region is invisible to human
eyes. Therefore, the risk is increased. In contrast, in a case where the
laser diode 3 is a laser diode that emits a laser beam having a
wavelength of 400 nm or greater, it can be easy to visually detect the
laser beam emitted from the laser diode. Therefore, even if a leakage of
the laser beam occurs, it is easy to deal with the leakage.

[0121] On the other hand, a risk caused by viewing light having no
coherence is as low as a risk caused by viewing normal light (which is
incoherent light as compared to coherent light), even if the light has
the same wavelength as that of the laser beam. Therefore, even in a case
of viewing a laser beam having a wavelength of 400 nm or greater but not
greater than 420 nm, it is not necessarily dangerous to human eyes

[0122] In the present embodiment, the laser beam emitted from the laser
diode 3, which is a coherent laser beam, is normally directed to the
light emitting section 7 and absorbed by the fluorescent material
contained in the light emitting section 7. Then, the laser beam thus
absorbed is converted in wavelength by the fluorescent material and
emitted therefrom as fluorescence having a longer wavelength than that of
the laser beam. At that time, the coherence of the laser beam is lost,
and the laser beam becomes incoherent fluorescence.

[0123] Further, a part of the coherent laser beam emitted from the laser
diode 3 loses the coherence by being subjected to scattering by particles
of the fluorescent material. In this way, the part of the coherent laser
beam becomes an incoherent laser beam, even in a case of not being
converted in wavelength by the fluorescent material.

[0124] Further, even if some of the coherent laser beam emitted from the
laser diode 3 do not lose the coherence and maintains to be coherent, the
laser beam maintaining the coherence is blocked and absorbed by the
excitation-light output prevention film 12 before the laser beam is
emitted outside the headlamp 1. This assures safety.

[0126] As described earlier, the headlamp 1 is designed such that the
bundle of beams formed by the reflection mirror 8 is outwardly emitted
from the headlamp 1 via the front end section 11a of the housing 11. This
indicates that outside light can enter the headlamp 1 from the outside of
the headlamp 1 via the front end section 11a of the housing 11.

[0128] In order to deal with this problem, the headlamp 1 in accordance
with the present embodiment has the excitation-light output prevention
film 12 attached to the front end section 11a of the housing 11, thereby
blocking entrance of the outside light.

[0129] For example, in a case where the laser diode 3 of the headlamp 1 in
accordance with the present embodiment is a one which emits a laser beam
with a wavelength of 400 nm or greater but not more than 420 nm, the
optical film constituting the excitation-light output prevention film 12
is designed to have the light cutting layer 12b which blocks light with a
wavelength of not more than 420 nm.

[0130] In this case, outside light with a wavelength of not more than 420
nm is blocked by the excitation-light output prevention film 12, and
consequently light does not enter the headlamp 1 from the outside thereof
through the front end section 11a of the housing 11.

[0131] Accordingly, the light emitting section 7 does not emit light upon
irradiation with the outside light. This prevents the light emitting
section 7 from unnecessarily emitting light. This prevents deterioration
of the light emitting section 7.

[0132] [Effect Yielded by Headlamp 1]

[0133] In the headlamp 1 designed as above, in a case where the front area
of the light emitting section 7 is 3 mm2 and the opening area of the
reflection mirror 8 is 2000 mm2, emitting a laser beam of 10 W from
the light output surface 22 of the light guide section 2 causes a light
flux of approximately 900 lm to be emitted and causes the light emitting
section 7 to exhibit luminance of 75 cd/mm2.

[0135] As described earlier, the excitation-light output prevention film
12 may be an absorbing film or a scattering film, or a combination
thereof.

[0136] With reference to FIG. 1, the following describes another
disposition of the excitation-light output prevention film 12.

[0137] As shown in FIG. 1, in a case where the excitation-light output
prevention film 12 is an absorbing film, the excitation-light output
prevention film 12 is attached to the front end section 11a of the
housing 11.

[0138] The excitation-light output prevention film 12 may be alternatively
attached to the transparent plate 9 covering the opening of the
reflection 8, for example.

[0139] Alternatively, the excitation-light output prevention film 12 may
be attached adjacently to the light emitting surface 7b of the light
emitting section 7 (surface of the light emitting section 7 which is
closer to the output side of the headlamp 1). In this case, an
absorbing-film attaching member should be provided adjacently to the
light emitting surface 7b of the light emitting section 7, and the
absorbing film should be attached to the absorbing-film attaching member.

[0140] The excitation-light output prevention film 12 may be alternatively
attached to both the front end section 11a of the housing 11 and the
transparent plate 9 or to both the front end section 11a of the housing
11 and the light emitting surface 7b of the light emitting section 7.
That is, the excitation-light output prevention film 12 should be made up
of two absorbing films, and one of the two absorbing films (first
absorbing member) should be attached to the transparent plate 9 or the
light emitting surface 7b of the light emitting section 7, and the other
of the two absorbing films (second absorbing member) should be attached
to the front end section 11a of the housing 11.

[0141] In either case, it can be said that the excitation-light output
prevention film 12 is positioned, with respect to the light emitting
section 7, to be closer to the output side of the headlamp 1.

[0142] On the other hand, in a case where the excitation-light output
prevention film 12 is a scattering film, the excitation-light output
prevention film 12 may be attached to the transparent plate 9 covering
the opening of the reflection mirror 8, for example.

[0143] Alternatively, the excitation-light output prevention film 12 may
be provided adjacently to the light emitting surface 7b of the light
emitting section 7 or the laser beam irradiation surface 7a of the light
emitting section 7. In this case, a scattering-film attaching member
should be provided adjacently to the light emitting surface 7b or the
laser beam irradiation surface 7a of the light emitting section 7, and
the scattering film should be attached to the scattering-film attaching
member.

[0144] In a case where the excitation-light output prevention film 12 is
provided adjacently to the light emitting surface 7b, it can be said that
the excitation-light output prevention film 12 is positioned, with
respect to the light emitting section 7, to be closer to the output side
of the headlamp 1. On the other hand, in a case where the
excitation-light output prevention film 12 is provided adjacently to the
laser beam irradiation surface 7a, it can be said that the
excitation-light output prevention film 12 is positioned, with respect to
the light emitting section 7, to be closer to a laser-diode-3-side of the
headlamp 1.

[0145] The excitation-light output prevention film 12 may be alternatively
attached to both the front end section 11a of the housing 11 and the
transparent plate 9 or to both the front end section 11a of the housing
11 and the light emitting surface 7b of the light emitting section 7.
Alternatively, the excitation-light output prevention film 12 may be
attached to both the front end section 11a of the housing 11 and the
laser beam irradiation surface 7a of the light emitting section 7.

[0146] In a case where the excitation-light output prevention film 12 is
made up of the absorbing film and the scattering film, the scattering
film and the absorbing film should be positioned so that the laser beam
emitted from the laser diode 3 enters the scattering film and the
absorbing film in this order. With this, even in a case where the
scattering film fails to completely scatter excitation light having
coherence, the absorbing film can absorb the excitation light.

Embodiment 2

[0147] Embodiment 2 of the present invention is described below. FIG. 5 is
a view schematically showing a configuration of a headlamp in accordance
with Embodiment 2 of the present invention. Hereinafter, members similar
to the members discussed in Embodiment 1 of the present invention are
given same reference signs, and their explanations are omitted.

[0148] A headlamp 1c in accordance with the present embodiment is
different from the headlamp 1 in accordance with Embodiment 1 in that a
light emitting section 7 is replaced with three light emitting sections
71, 72, and 73.

[0149] In the headlamp 1 in accordance with Embodiment 1, there may be
used the laser diode 3 which emits a laser beam with a wavelength of 400
nm or greater but not more than 420 nm. In this case, a laser beam with a
wavelength of approximately 405 nm which is the wavelength of the
excitation light is blocked by the excitation-light output prevention
film 12.

[0150] Consequently, in a case where the fluorescent material contained in
the light emitting section 7 is a simple mixture of a green fluorescent
material (e.g. Caα-SiAlON: Ce) and a red fluorescent material (e.g.
CASN: Eu, SCASN: Eu), a white light derived from fluorescent lights
respectively from the fluorescent materials has a small controllable
range of chromaticity since light with a wavelength of approximately 405
nm is blocked as above.

[0151] In order to deal with this problem, the headlamp 1c in accordance
with the present embodiment is designed to include not only a light
emitting section 71 containing a green fluorescent material (e.g.
Caα-SiAlON: Ce mentioned above) and a light emitting section 72
containing a red fluorescent material (e.g. CASN: Eu, SCASN: Eu mentioned
above) but also a light emitting section 73 containing a blue fluorescent
material.

[0152] An example of the blue fluorescent material contained in the light
emitting section 73 is an oxynitride fluorescent material containing JEM
(JEM phase fluorescent material). The JEM phase fluorescent material is a
material which is confirmed to be produced in a process of controlling a
stable sialon fluorescent material by a rare earth element. The JEM phase
is ceramics which was found as a grain boundary phase of a silicon
nitride material, and is a crystalline phase (oxynitride crystal) having
a unique atom sequence generally represented by composition formula
M1Al (Si6-zAlz)N10-zOz wherein M1 is at
least one element selected from the group consisting of La, Ce, Pr, Nd,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and z is a parameter. The JEM
phase has a strong covalent bond between crystals and so is excellent in
heat resistance. An example of the JEM fluorescent material is LaSiAlON:
Ce. When the JEM fluorescent material contains a Ce component, it gets
easier to realize emission ranging from blue to blue-green. When an
excitation wavelength is 405 nm, the JEM phase: Ce fluorescent material
has a peak wavelength of 490 nm and an emission efficiency of 50%.

[0153] In the headlamp 1c in accordance with the present embodiment, there
are provided three light emitting sections: the light emitting sections
71, 72, and 73. Alternatively, there may be provided only one light
emitting section in which the aforementioned three fluorescent materials
(green fluorescent material, red fluorescent material, and blue
fluorescent material) are mixed with one another and dispersed.

[0154] (Structure of Laser Diode 3)

[0155] The following describes a basic structure of the laser diode 3 for
use in the headlamp 1 in accordance with Embodiment 1 and the headlamp 1c
in accordance with Embodiment 2. FIG. 6(a) is a circuit view showing the
laser diode 3. FIG. 6(b) is a perspective view showing the basic
structure of the laser diode 3. As shown in FIG. 6(b), the laser diode 3
includes a cathode electrode 19, a substrate 18, a clad layer 113, an
active layer 111, a clad layer 112, and an anode electrode 17, which are
stacked in this order.

[0156] The substrate 18 is a semiconductor substrate. The substrate 18 is
generally made from a compound semiconductor such as GaAs or GaN. The
substrate 18 may be alternatively made from (i) a IV group semiconductor
such as Si, Ge, and SiC, (ii) a III-V group compound semiconductor such
as GaAs, GaP, InP, AlAs, GaN, InN, InSb, GaSb, and AlN, (iii) a II-VI
group compound semiconductor such as ZnTe, ZeSe, ZnS, and ZnO, (iv) an
oxide insulator such as ZnO, Al2O3, SiO2, TiO2,
CrO2, and CeO2, or (v) a nitride insulator such as SiN. It is
preferable that the substrate 18 is made from the nitride semiconductor
in particular.

[0157] The anode electrode 17 is provided for injecting an electric
current into the active layer 111 via the clad layer 112.

[0158] The cathode electrode 19 is provided for injecting a current into
the active layer 111 via the clad layer 113 from under the substrate 18.
The current is injected by applying a forward bias to the anode electrode
17 and the cathode electrode 19.

[0159] The active layer 111 is sandwiched between the clad layer 113 and
the clad layer 112.

[0160] A material of the active layer 111 may be (i) a III-V group
compound semiconductor such as undoped GaAs, GaP, InP, AlAs, GaN, InN,
InSb, GaSb, and AlN or (ii) a II-VI group compound semiconductor such as
ZnTe, ZeSe, ZnS, and ZnO.

[0161] The active layer 111 is a region where light emission is caused by
the injection of the current. Emitted light is trapped within the active
layer 111 due to differences in refractive index between the active layer
111 and the clad layers 112 and 113.

[0162] Furthermore, the active layer 111 has a front cleaved surface 114
and a rear cleaved surface 115 which face each other so as to trap light
amplified by stimulated emission. The front cleaved surface 114 and rear
cleaved surface 115 serve as mirrors.

[0163] However, unlike mirrors which totally reflect light, light is
amplified by induced emission in the active layer 111, and when the light
is amplified to some extent, the light is outputted via one of the front
cleaved surface 114 and the rear cleaved surface 115 (for convenience of
explanation, it is assumed that the light is outputted via the front
cleaved surface 114 in the present embodiment) and becomes a laser beam
(excitation light) L0. The active layer 111 can have a multilayer quantum
well structure.

[0164] The back cleavage surface 115, which faces the front cleavage
surface 114, has a reflection film (not illustrated) for laser
oscillation. By differentiating reflectance of the front cleavage surface
114 from reflectance of the back cleavage surface 115, it is possible for
the excitation light L0 to be emitted from a luminous point 103 of an end
surface having low reflectance (e.g., the front cleavage surface 114).

[0165] Each of the clad layer 113 and the clad layer 112 can be
constituted by: n-type and p-type III-V group compound semiconductors
such as that made of GaAs, GaP, InP, AlAs, GaN, InN, InSb, GaSb, or AlN;
or n-type and p-type II-VI group compound semiconductors such as that
made of ZnTe, ZeSe, ZnS, or ZnO. The electrical current can be injected
into the active layer 111 by applying forward bias to the anode electrode
17 and the cathode electrode 19.

[0166] A semiconductor layer such as the clad layer 113, the clad layer
112, and the active layer 111 can be formed by a commonly known film
formation method such as MOCVD (metal organic chemical vapor deposition),
MBE (molecular beam epitaxy), CVD (chemical vapor deposition),
laser-ablation, or sputtering. Each metal layer can be formed by a
commonly known film formation method such as vacuum vapor deposition,
plating, laser-ablation, or sputtering.

[0167] (Principle of Light Emission of Light emitting section 7)

[0168] Next, the following description discusses a principle of a
fluorescent material emitting light upon irradiation with a laser beam
emitted from the laser diode 3.

[0169] First, the fluorescent material contained in the light emitting
section 7 is irradiated with the laser beam emitted from the laser diode
3. Upon irradiation with the laser beam, an energy state of electrons in
the fluorescent material is excited from a low energy state into a high
energy state (excitation state).

[0170] After that, since the excitation state is unstable, the energy
state of the electrons in the fluorescent material returns to the low
energy state (an energy state of a ground level, or an energy state of an
intermediate metastable level between ground and excited levels) after a
certain period of time.

[0171] As described above, the electrons excited to be in the high energy
state returns to the low energy state. In this way, the fluorescent
material emits light.

[0172] Note here that, white light can be made by mixing three colors
which meet the isochromatic principle, or by mixing two colors which are
complimentary colors for each other. The white light can be obtained by
combining (i) a color of the laser beam emitted from the laser diode 3
and (ii) a color of the light emitted from the fluorescent material on
the basis of the foregoing principle and relation.

Embodiment 3

[0173] The following explains another embodiment of the present invention
with reference to FIGS. 7-12. Members similar to those in Examples 1 and
2 are given the same reference numerals and explanations thereof are
omitted here.

[0174] An explanation is made here as to a laser downlight 200 which is an
example of an illuminating equipment of the present invention. The laser
downlight 200 is an illuminating equipment to be installed into a ceiling
of a structure such as a house and a vehicle. The laser downlight 200
uses, as illumination light, fluorescence generated when the light
emitting section 7 is irradiated with a laser beam emitted from the laser
diodes 3.

[0175] An illuminating equipment having a configuration similar to that of
the laser downlight 200 may be installed into a side wall or a floor of a
structure. Where the illuminating equipment is installed is not
particularly limited.

[0176]FIG. 7 is a view schematically illustrating appearances of a light
emitting unit 210 and a conventional LED downlight 300. FIG. 8 is a cross
sectional view illustrating a ceiling where the laser downlight 200 is
installed. FIG. 9 is a cross sectional view of the laser downlight 200.
As illustrated in FIGS. 7-9, the laser downlight 200 includes the light
emitting unit 210 which is embedded in a ceiling panel 400 and emits
illumination light, and an LD light source unit 220 which supplies a
laser beam to the light emitting unit 210 via an optical fiber 5. The LD
light source unit 220 is not installed into the ceiling but is installed
at a position where a user can easily touch the LD light source unit 220
(e.g. side wall of a house). The position of the LD light source unit 220
can be freely determined as above because the LD light source unit 220
and the light emitting unit 210 are connected with each other via the
optical fiber 5. The optical fiber 5 is provided at a space between the
ceiling 400 and a thermal insulator 401.

[0177] (Configuration of Light Emitting Unit 210)

[0178] As illustrated in FIG. 9, the light emitting unit 210 includes a
housing 211, the optical fiber 5, the light emitting section 7, and a
transparent plate 213.

[0179] The housing 211 has a recess 212. The light emitting section 7 is
provided on a bottom surface of the recess 212. The recess 212 is coated
with a metal thin film so as to serve as a reflection mirror.

[0180] Further, the housing 211 has a path 214 via which the optical fiber
5 extends to the light emitting section 7. A positional relationship
between an output end part of the optical fiber 5 and the light emitting
section 7 is similar to the one described above.

[0181] The transparent plate 213 is a transparent or semi-transparent
plate positioned in such a manner as to seal an opening of the recess
212. The transparent plate 213 has the same function as the transparent
plate 9. Fluorescence emitted from the light emitting section 7 passes
through the transparent plate 213 and is emitted as illumination light.
The transparent plate 213 may be removable from the housing 211 or may be
omitted.

[0182] An optical film (not shown) having a function similar to that of
the excitation-light output prevention film 12 is attached to the
internal surface or the outer surface of the transparent plate 213.

[0183] In FIG. 7, the light emitting unit 210 has a circularly shaped
outer periphery. However, the shape of the light emitting unit 210 (to be
more exact, the shape of the housing 211) is not particularly limited.

[0184] It should be noted that a downlight is not required to have an
ideal point light source unlike a headlamp, and is only required to have
one luminous point. Therefore, the shape, the size, and the position of
the light emitting section 7 are less limited than those of a headlamp.

[0187] An entrance end part, which is one end of the optical fiber 5, is
connected with the LD light source unit 220. A laser beam emitted from
the laser diode 3 enters the entrance end part of the optical fiber 5 via
the aspheric lens 4.

[0188]FIG. 9 shows that only one pair of the laser diode 3 and the
aspheric lens 4 is provided in an inside of the LD light source unit 220.
In a case where a plurality of light emitting units 210 are provided, a
bundle of optical fibers 5 respectively extended from the plurality of
light emitting units 210 may be led to one LD light source unit 220. In
this case, one LD light source unit 220 includes plural pairs of the
laser diode 3 and the aspheric lens 4 and thereby serves as an integrated
power source box.

[0189] (Modification Example of Installation of Laser Downlight 200)

[0190]FIG. 10 is a cross sectional view showing a modification example of
installation of the laser downlight 200. As shown in FIG. 10, the laser
downlight 200 may be installed in a modified manner described as follows.
By taking advantages of characteristics such as thinness and light
weight, a laser downlight main body (the light emitting unit 210) may be
attached to a ceiling 400 having only a fine hole 402 for allowing the
optical fiber 5 to run therethrough. This configuration is advantageous
in that installation of the laser downlight 200 is less restricted and
costs for the installation can be greatly reduced.

[0192] As shown in FIG. 7, the conventional LED downlight 300 includes a
plurality of transparent plates 301, and illumination light is emitted
via the individual transparent plates 301. That is, the LED downlight 300
has a plurality of luminous points. The reason why the LED downlight 300
has the plurality of luminous points is that luminous flux of light
emitted from the individual luminous points is relatively small and so a
plurality of luminous points must be provided in order to assure light
with luminous flux sufficient as illumination light.

[0193] In contrast thereto, the laser downlight 200 is an illuminating
equipment that emits light of a high luminous flux. Therefore, the number
of a luminous point for the laser downlight 200 may be one. This yields
an effect that illumination light makes shades and shadows clear.
Further, by using high color rendering fluorescent materials (e.g. a
combination of plural kinds of oxynitride fluorescent material and/or
nitride fluorescent material) as a fluorescent material of the light
emitting section 7, it is possible to improve color rendering properties
of illumination light.

[0194] This enables achieving high color rendering almost equal to that of
an incandescent bulb. For example, light with high color rendering
(general color rendering index Ra is 90 or more and special color
rendering index R9 is 95 or more) which is difficult to be achieved by an
LED downlight or a fluorescent lamp downlight can be achieved by
combining a high color rendering fluorescent material with the laser
diode 3.

[0195] FIG. 11 is a cross sectional view of a ceiling to which LED
downlights 300 are installed. As shown in FIG. 11, in each of the LED
downlights 300, a housing 302 which houses an LED chip, a power source,
and a cooling unit therein is embedded in the ceiling plate 400. The
housing 302 is relatively large. A heat insulator 401 has a recess whose
shape corresponds to the shape of the housing 302 and on which the
housing 302 is positioned. A power source line 303 is extended from the
housing 302 and connected with an outlet (which is not shown).

[0196] Such configuration gives a rise to the following problems. First of
all, because a light source (LED chip) and a power source, which generate
heat, are provided between the ceiling panel 400 and the heat insulator
401, use of the LED downlight 300 causes an increase in temperature of
the ceiling, which reduces an efficiency of cooling the room.

[0197] Secondly, because the LED downlight 300 requires a power source and
a cooling unit for each light source, total costs are increased.

[0198] Thirdly, because the housing 302 is relatively large, it is often
difficult to provide the LED downlight 300 between the ceiling panel 400
and the heat insulator 401.

[0199] In contrast, in the laser downlight 200, the light emitting unit
210 does not include a large heat source. As such, use of the laser
downlight 200 does not cause a reduction in the efficiency of cooling the
room. This enables avoiding an increase in costs for cooling the room.

[0200] Further, in the laser downlight 200, it is unnecessary to provide a
power source and a cooling unit for each light emitting unit 210. Thus,
the laser downlight 200 can be small and thin. This reduces a restriction
on a space where the laser downlight 200 is installed, and thereby makes
it easier to install the laser downlight 200 into an existing house.

[0201] Further, because the laser downlight 200 is small and thin, the
light emitting unit 210 can be provided on the surface of the ceiling
400, as described above. This enables reducing a restriction on
installation of the laser downlight 200 and greatly reducing costs for
the installation, as compared with installation of the LED downlight 300.

[0202]FIG. 12 is a table in which specifications of the laser downlight
200 and those of the LED downlight 300 are compared with each other. As
shown in FIG. 12, in one example, a volume of the laser downlight 200 is
smaller by 94% than that of the LED downlight 300 and a mass of the laser
downlight 200 is smaller by 86% than that of the LED downlight 300.

[0203] Because the LD light source unit 220 can be installed at a place
where a user can easily reach, it is possible to easily change the laser
diode 3 when the laser diode 3 is in trouble. Further, by leading the
optical fibers 5 respectively extended from the plurality of light
emitting units 210 to one LD light source unit 220, it is possible to
manage the plurality of laser diodes 3 at once. Therefore, even when two
or more laser diodes 3 are to be replaced with new ones, it is possible
to easily replace them.

[0204] In a case where the LED downlight 300 employs a high color
rendering fluorescent material, the LED downlight 300 can emit a luminous
flux of approximately 500 μm at a power consumption of 10 W. However,
in order for the laser downlight 200 to emit a laser beam of same
luminance, an optical output of 3.3 W is required. The optical output of
3.3 W corresponds to a power consumption of 10 W in a case where LD
efficiency is 35%. Because the power consumption of the LED downlight is
10 W, there is no significant difference in power consumption between the
laser downlight 200 and the LED downlight 300. Therefore, the laser
downlight 200 enjoys various advantages as above, with the same power
consumption as that of the LED downlight 300.

[0205] As described above, the laser downlight 200 includes (i) the LD
light source unit 220 including at least one laser diode 3 for emitting a
laser beam, (ii) at least one light emitting unit 210 including the light
emitting section 7, the transparent plate 213 to which the optical film
having the function similar to the excitation-light output prevention
film 12 is attached, and the recess 212 serving as a reflection mirror,
and (iii) the optical fiber 5 which directs the laser beam to the at
least one light emitting unit 210.

[0206] The present invention is not limited to the description of the
embodiments above, but may be altered by a skilled person within the
scope of the claims. An embodiment based on a proper combination of
technical means disclosed in different embodiments is encompassed in the
technical scope of the present invention.

OTHER DESCRIPTION OF THE PRESENT INVENTION

[0207] The present invention may be described as follows.

[0208] It is preferable to arrange the light emitting device of the
present invention such that the excitation light output prevention member
includes an absorbing member for absorbing the excitation light with
coherence, and the absorbing member is positioned in a vicinity of the
light emitting section in such a manner as to be closer to an output side
of the light emitting device.

[0209] With the arrangement, the absorbing member can absorb excitation
light (i) with which the light emitting section is not irradiated or (ii)
with which the light emitting section is irradiated but which is neither
absorbed nor scattered by the fluorescent material contained in the light
emitting section and consequently is outputted from the light emitting
section without any change while maintaining coherence.

[0210] Accordingly, it is possible to completely prevent the excitation
light with coherence from being outputted outside the light emitting
device.

[0211] It is preferable to arrange the light emitting device of the
present invention so as to further include a mortar-shaped reflection
mirror for reflecting the light emitted by the light emitting section so
that the light is directed toward the output side of the light emitting
device, the light emitting section being positioned inside the
mortar-shaped reflection mirror, and the absorbing member being
positioned inside the mortar-shaped reflection mirror in such a manner as
to be in a vicinity of one surface of the light emitting section which
one surface is closer to the output side of the light emitting device.

[0212] With the arrangement, since the absorbing member is in a vicinity
of one surface of the light emitting section which one surface is closer
to the output side of the light emitting device, excitation light which
has not been used in emission of light and has passed through the
absorbing member can be directed by the mortar-shaped reflection mirror
to the output side of the light emitting device.

[0213] Therefore, it is possible to increase a utilization ratio of the
excitation light, thereby increasing light outputted from the light
emitting device.

[0214] It is preferable to arrange the light emitting device of the
present invention so as to further include a mortar-shaped reflection
mirror for reflecting the light emitted by the light emitting section so
that the light is directed toward the output side of the light emitting
device, the light emitting section being positioned inside the
mortar-shaped reflection mirror, and the absorbing member being
positioned outside the mortar-shaped reflection mirror.

[0215] With the arrangement, since the absorbing member is positioned
outside the mortar-shaped reflection mirror, the absorbing member can be
positioned, for example, on the light emitting surface of a housing for
housing the reflection mirror.

[0216] It is preferable to arrange the light emitting device of the
present invention so as to further include a housing for housing the
reflection mirror, the housing having (i) a light emitting surface for
emitting light coming from the reflection mirror toward the output side
of the light emitting device, and (ii) a light blocking surface for
blocking light coming from the reflection mirror toward a direction
different from a direction toward the output side of the light emitting
device, and the absorbing member being positioned on the light emitting
surface of the housing.

[0217] With the arrangement, since the absorbing member is positioned
outside the mortar-shaped reflection mirror, the absorbing member can be
positioned on the light emitting surface of the housing for housing the
reflection mirror.

[0218] It is preferable to arrange the light emitting device of the
present invention so as to further include: a mortar-shaped reflection
mirror for reflecting the light emitted by the light emitting section so
that the light is directed toward the output side of the light emitting
device; and a housing for housing the reflection mirror, the absorbing
member including a first absorbing member and a second absorbing member,
the light emitting section being positioned inside the mortar-shaped
reflection mirror, the first absorbing member being positioned in a
vicinity of the light emitting section in such a manner as to be closer
to the output side of the light emitting device, the housing having (i) a
light emitting surface for emitting light coming from the reflection
mirror toward the output side of the light emitting device, and (ii) a
light blocking surface for blocking light coming from the reflection
mirror toward a direction different from a direction toward the output
side of the light emitting device, and the second absorbing member being
positioned on the light emitting surface of the housing.

[0219] With the arrangement, since the absorbing member is twofold, it is
possible to secure safety sufficiently.

[0220] It is preferable to arrange the light emitting device of the
present invention such that the first absorbing member is positioned
inside the mortar-shaped reflection mirror in such a manner as to be in a
vicinity of one surface of the light emitting section which one surface
is closer to the output side of the light emitting device.

[0221] With the arrangement, since the absorbing member is in a vicinity
of one surface of the light emitting section which one surface is closer
to the output side of the light emitting device, excitation light having
passed through the absorbing member without being used in emission of the
light emitting section can be directed by the mortar-shaped reflection
mirror to the output side of the light emitting device.

[0222] Therefore, it is possible to increase a utilization ratio of the
excitation light, thereby increasing light outputted from the light
emitting device.

[0223] It is preferable to arrange the light emitting device of the
present invention such that the excitation light output prevention member
includes a scattering member for scattering the excitation light with
coherence.

[0224] With the arrangement, the scattering member can scatter (a)
excitation light with which the light emitting section is not yet
irradiated and which maintains coherence or (b) excitation light with
which the light emitting section is not irradiated or excitation light
with which the light emitting section is irradiated but which is neither
absorbed nor scattered by the fluorescent material contained in the light
emitting section so that the excitation light is outputted from the light
emitting section without any change and consequently maintains coherence.
Accordingly, it is possible to output the excitation light to the outside
of the light emitting device after the excitation light has been
converted to have incoherence.

[0225] Accordingly, it is possible to prevent the excitation light with
coherence from being outputted outside the light emitting device.

[0226] It is preferable to arrange the light emitting device of the
present invention so as to further include a mortar-shaped reflection
mirror for reflecting the light emitted by the light emitting section so
that the light is directed toward an output side of the light emitting
device, the light emitting section being positioned inside the
mortar-shaped reflection mirror, and the scattering member being
positioned inside the mortar-shaped reflection mirror in such a manner as
to be in a vicinity of one surface of the light emitting section which
one surface is closer to the output side of the light emitting device.

[0227] With the arrangement, the scattering member is in a vicinity of one
surface of the light emitting section which one surface is closer to the
output side of the light emitting device. Accordingly, excitation light
which has not been used in emission of the light emitting section and has
been scattered by the scattering member to be converted to have
incoherence can be directed by the mortar-shaped reflection mirror to the
output side of the light emitting device.

[0228] Therefore, it is possible to increase a utilization ratio of the
excitation light, thereby increasing light outputted from the light
emitting device.

[0229] It is preferable to arrange the light emitting device of the
present invention such that the scattering member is positioned in a
vicinity of the light emitting section in such a manner as to be closer
to the excitation light source, and the scattering member scatters
excitation light coming from the excitation light source toward the light
emitting section, and the light emitting section is irradiated with the
excitation light scattered by the scattering member.

[0230] With the arrangement, it is possible to convert all the excitation
light with coherence coming from the excitation light source into
excitation light with incoherence before it reaches the light emitting
section.

[0231] Consequently, the light emitting section is irradiated with only
excitation light with incoherence. Accordingly, even if some excitation
light is neither absorbed nor scattered by the fluorescent material
contained in the light emitting section and is outputted from the light
emitting section without any change, the excitation light does not have
coherence.

[0232] Accordingly, it is possible to surely prevent excitation light with
coherence from being outputted from the light emitting device without any
change.

[0233] It is preferable to arrange the light emitting device of the
present invention such that the excitation light output prevention member
further includes an absorbing member for absorbing the excitation light
with coherence, the excitation light from the excitation light source
enters the scattering member and the absorbing member in this order, and
the absorbing member absorbs excitation light coming from the excitation
light source toward the output side of the light emitting device
regardless of whether the light emitting section is irradiated with the
excitation light.

[0234] With the arrangement, eve if the scattering member cannot
completely scatter the excitation light with coherence, it is possible
for the absorbing member to absorb the excitation light.

[0235] Accordingly, it is possible to prevent the excitation light with
coherence from being outputted outside the light emitting device.

[0236] It is preferable to arrange the light emitting device of the
present invention such that the light emitting section includes a green
light emitting portion for emitting green light, a red light emitting
portion for emitting red light, and a blue light emitting portion for
emitting blue light.

[0237] When light emitted from the light emitting section passes through
the absorbing member for absorbing excitation light, partial light with a
wavelength to be absorbed by the absorbing member is also absorbed. This
changes the color of the light emitted from the light emitting section.

[0238] In order to deal with this problem, the light emitting section with
the above arrangement is designed so as to include a green light emitting
portion for emitting green light, a red light emitting portion for
emitting red light, and a blue light emitting portion for emitting blue
light so that the green light emitted from the green light emitting
portion, the red light emitted from the red light emitting portion, and
the blue light emitted from the blue light emitting portion are mixed
with one another.

[0239] In a case where light which is a mixture of lights from the three
light emitting sections passes through the absorbing member for absorbing
excitation light, even when the light is partially absorbed as described
above, a change in the color of light due to absorption of the partial
light can be subdued by controlling intensities of individual lights from
the three light emitting sections beforehand.

[0240] It is preferable that an illuminating equipment in accordance with
one embodiment of the present invention includes the aforementioned light
emitting device.

[0241] With the arrangement, since the illuminating equipment includes the
aforementioned light emitting device as a light source, the illuminating
equipment can prevent excitation light with coherence from being
outputted outside.

[0242] A vehicle headlamp in accordance with one embodiment of the present
invention includes the aforementioned light emitting device.

[0243] With the arrangement, since the vehicle headlamp includes the
aforementioned light emitting device as a light source, the vehicle
headlamp can prevent excitation light with coherence from being outputted
outside.

[0244] The present invention is not limited to the description of the
embodiments above, but may be altered by a skilled person within the
scope of the claims. That is, an embodiment based on a combination of
technical means modified as needed within the scope of the claims is
encompassed in the technical scope of the present invention.

INDUSTRIAL APPLICABILITY

[0245] The present invention is a light emitting device that emits light
of high luminance and high luminous flux but is smaller than a
conventional light emitting device. The present invention can be applied
to a vehicle headlamp, a projector, and the like.